The $150k is not what your work is directly valued at, but rather an agreement of what it'll take for you to drag your ass to San Francisco, which is objectively a bad place to live if you're a human that has to make budgets, and come to work at Facebook.
Also yes, if Facebook starts to hire remote workers, then your value will drop because they now have the access to a pool of workers who don't want to drag their asses to San Francisco and can pretty easily settle for less since their rent doesn't require them to bleed money.
Also yes, if Facebook starts to hire remote workers, then your value will drop because they now have the access to a pool of workers who don't want to drag their asses to San Francisco and can pretty easily settle for less since their rent doesn't require them to bleed money.